Great idea and I've 'registered' already. I think it will be very popular from both sides.
The one problem I can see is this. Most of the really experienced players tend to play in all the game worlds (except Beginners World of course - and they would if they could
) so it may be difficult for a newish player to find a good mentor when they begin their first REAL game world. And I think that's the time when they're most likely to need help.
I can see why there is the limitation - no mentoring in a world you're playing in, but really - would someone who's willing to offer their time end experience really not do their best for the mentee (?). I've even helped people in the past who I've been in direct competition with. I'd like to think that we're a friendly bunch here and none of us would abuse the position, but maybe I'm over-trusting and naive. Dunno.
How about a limit that you CAN mentor in a world you're playing, but only an airline based in a different country - or even a different continent. Yes there may be one or two routes of competition, between the two bases, but so what!